This invention relates generally to gas concentration apparatus for separating gas mixtures by pressure swing adsorption (xe2x80x9cPSAxe2x80x9d) and more particularly to PSA apparatus intended to deliver oxygen for medical use.
The general type and operating principles of PSA, or pressure swing adsorption, apparatus with which this invention is concerned are described in U.S. Pat. Nos. 3,564,816; 3,636,679; 3,717,974; 4,802,899; 5,531,807 and 5,871,564, among others. For example, a pressure swing adsorption apparatus may include one or more adsorbers, each having a fixed sieve bed of adsorbent material to fractionate at least one constituent gas from a gaseous mixture by adsorption into the bed, when the gaseous mixture from a feed stream is sequentially directed through the adsorbers in a co-current direction. While one adsorber performs adsorption, another adsorber is simultaneously purged of its adsorbed constituent gas by part of the product gas that is withdrawn from the first or producing adsorber and directed through the other adsorber in a counter-current direction. Once the other adsorber is purged, the feed stream at a preset time is then directed to the other adsorber in the co-current direction, so that the other adsorber performs adsorption. The first adsorber then is purged either simultaneously, or in another timed sequence if there are more than two adsorbers, all of which will be understood from a reading of the above described patents.
When, for example, such apparatus is used to produce a high concentration of oxygen from ambient air for use in various applications, whether medical, industrial or commercial, air which enters the apparatus typically contains about 78% nitrogen, 21% oxygen, 0.9% argon, and a variable amount of water vapor. Principally, most of the nitrogen is removed by the apparatus to produce a gas product, which for medical purposes, for example, typically may contain at least about 80% oxygen. Most such apparatus for medical uses generally are too bulky for use by patients who are traveling or otherwise wish to leave their home environments for any purpose. In those cases, patients will normally forego the use of oxygen concentrators and revert to the use of pressurized oxygen tanks. While oxygen tanks have been very useful in enabling patients to be more ambulatory, they nevertheless are restricted in use, as for example because of limited oxygen storage capacity or because their use may be prohibited in certain modes of public transportation or locations where flammable materials can create a hazard. Although the useful life of oxygen tanks may be extended by the use of oxygen concentration devices (xe2x80x9cOCDxe2x80x9d), as disclosed, for example, in co-pending U.S. application Ser. No. 09/420,826, filed Oct. 19, 1999, their use nevertheless continues to be problematic because of safety and storage concerns, access to re-supplies of oxygen, and continuing medical expenses and reimbursement paperwork for the oxygen.
The present invention provides a new and improved pressure swing adsorption (xe2x80x9cPSAxe2x80x9d or xe2x80x9coxygen concentratorxe2x80x9d) apparatus that can attain the required concentrations of oxygen for the desired application(s), yet be highly portable and easily manipulated and transported even by patients with relatively limited physical capacities. This is accomplished by a unique configuration combining an inventive PSA design with an oxygen conservation device (xe2x80x9cOCDxe2x80x9d) for pulse dose application of oxygen from the PSA to the user.
The intended use of the apparatus is to deliver supplemental, high-purity oxygen to persons who suffer, for example, from various forms of Chronic Obstructive Pulmonary Disease (COPD). The invention preferably uses a two-bed PSA together with an integrated OCD to provide oxygen in doses up to an equivalent of about 5 liters per minute (LPM) effective rate of continuous high-concentration oxygen at concentrations over 90%.